Pressure sensitive recording material and method of making same



United States Patent PRESSURE SENSITIVE RECORDING MATERIAL AND METHOD OF MAKING SAME Donald K. Werle, Franklin Park, and Michael Michalchik, Chicago, Ill., assignors, by mesne assignments, to UARCO Incorporated, a corporation of Illinois No Drawing. Filed Nov. 13, 1957, Ser. No. 696,036

12 Claims. (Cl. 117-36) tively dark-colored surface over which is adhered a pres- "sure sensitive opaque coating of contrasting color. The opaque coating or film "may become transparent upon the application of pressure from a stylus, typewriter key or similar instrument. In the past, the quality of coatings of this type have not been satisfactory for commercial use. 'The contrast between the opaque film and the areas in which pressure was applied has not been sufiicient to give legible copies of writing. The pressures required to crush the opaque film and make it transparent have generally been higher than those ordinarily encountered in business machines and typewriters. The making of one or two copies has been feasible but modern business methods often require many more copies than were feasible with the prior coated papers.

The present invention presents a much improved opaque film for a dark-colored paper. The film is quite sensitive to pressures normally encountered in typewriters, billing machines and as employed by persons using the normal writing instruments. The film has good aging properties and is resistant to heat and moisture that would normally be encountered during storage. Paper coated with the film may be handled without adverse eifects. In addition to the new coating, the invention includes steps for improving the quality of prior coatings.

It is the principalobject of this invention to provide a new and improved pressure sensitive recording material for manifolding and a method of manufacturing ,the same. Another object is to provide a method of forming pres- USUIQSfiIlSitiVB record material which comprises applying .a film including a cellulose compound to the surface of a base sheet and drying the film in the presence of moisturewhich is condensed thereon to form an opaque light-colored blushed film sensitive to writing pressure.

": Other features, objects and advantages of the present invention will be apparent in the following specification.

re application of a film to a base sheet which prefery has a dark-coloredsurface. The film includes a humid atmosphere on the film. On drying, such a film 2,939,802 Patented June 7, 1960 is found to have an unusually satisfactory blushed surface which is high in light reflectivity and pressure sensitivity and which is particularly adapted for use as a pres sure sensitive manifolding paper.

The present invention utilizes cellulose compounds to produce satisfactory pressure sensitive blushed films. Among the cellulose compounds which are useful are cellulose esters including cellulose butyrate, cellulose oleate, cellulose stearate, cellulose phthalate, cellulose naphthenate, cellulose laurate, cellulose aceto-butyrate, cellulose aceto-maleate and cellulose aceto-nitrate; cellulose others including ethyl cellulose, benzyl cellulose, and glycol cellulose; and cellulose ether-esters, including ethyl cellulose-nitrate, benzyl cellulose-acetate, ethyl cellulose ace tate, and glycol cellulose-acetate. However, ethyl hyhydroxyethyl cellulose, ethyl cellulose, and nitro-celluloso are the preferred cellulose compounds with ethyl hydroxyethyl cellulose being most preferred.

In producing the pressure sensitive blushed film, the cellulose film is applied to a base sheet. which is generally paper and which is preferably provided with a dark-colored surface. Various types of paper may be used and it is only necessary that the tear strength of the paper be sufficient so that it can withstand the moisture present. For example, an 8 1b., 25% rag content,

sulfite paper has been found satisfactory for this purpose.

As previously pointed out, it is preferable that the paper have a dark-colored surface. The paper may be coated with a black coating, for example, to obtain the desiredresult. A flexographic type ink has been found to be satisfactory for this purpose. Such an ink includes a polyamide type resin which allows the cellulose film to adhere quite readily to the ink. Other precoat materials may also be used to provide a surface on the paper to which the cellulose film will quite readily adhere. For example, other polyamide resins may be used and other coatings such as animal glue, carboxymethyl celluloseand rubber cement are satisfactory for this purpose. Various other resins which are generally well-known in the art may also be used as a precoat and adhesive typematerial.

In compounding the cellulose films of this invention, it is necessary to provide solvents for the cellulose compounds. In this respect it is desirable to use organic type solvents which are compatible both with the cellulose compound and with water. However, in the event that a solvent is used which is compatible with the cellulose compound and not with water, a polar liquid may be added as is well-known in the art to give the desired water compatibility thus providing a solvent system. Among the solvents which are useful are benzene, acetone, ethyl ether, ethylene dichloride, carbon tetrachloride, toluene, dioxane, ethyl acetate, methyl ethyl ketone, ethanol, n-propanol, butyl acetate, methyl isobutyl ketone, xyleneor other similar cellulose derivative solvents. As previously stated, the use of the alcohol or ketone with a non-polar solvent for the cellulose compound is .rdesirable and .is primarily for the purpose of increasing the compatibility of water in the solution so that the water which condenses from the humid drying air is miscible with thewet film.

Theoretically, it is the presence of water in the cellulose-solvent system which will cause a film to blush. The amount of water necessary to cause the blushing in the process of this invention is provided by drying the film coated paper in a warm humid atmosphere so that the evaporating solvents will cool the surface of the paper thus causing the water from the air to condense thereon. It is also possible to place a small percentage of water in the film before it is applied to the surface of the paper. This tends to hasten the blushing time necessary in the humid air. However, too much water will cause the film to blush prematurely, and thus give undesirable results.

solution was achieved.

In general, the proportions of the cellulose compound, solvents and water, may be varied within the following ranges to achieve satisfactory results.

Percent by weight Total solvent 70-95 Non-polar solvent if necessary, of the total solvent 10-20 Cellulose compound 3-20 Water -10 ing examples:

Example I To a large size mixing kettle provided with an automatic stirrer was added lbs. of ethyl hydroxyethyl cellulose having viscosity of 27 centipoises, 12 lbs. of hen- 'zene, 79 lbs. of methyl alcohol and 4 lbs. of water.

These were thoroughly mixed together until a complete The wet solution was then applied by means of a roller to the surface of an 8 1b.,

25% rag content, sulfite paper having a dark-colored surface, such as previously mentioned. The volatile solvents in the wet film were then driven out by drying the :film in the presence of warm, humid air. The air was at about a temperature of 100 F. and at a 60% relative humidity and was passed over the film. As the volatile :solvents were driven out, the film was cooled considerably below ambient temperatures which caused moisture from the humid air to cendense upon the film. It has been found that the blushing is greatly improved by condensing the water upon the film since it is believed that the water concentration increases quite rapidly causing the ethyl hydroxyethyl cellulose to precipitate. When the coating was blushed in this manner with humid air a continuous, quite porous and thus much whiter coating was produced than was possible with the use of dry .air.

The more porous the coating, the faster the drying can. occur since remaining liquids after precipitation of the ethyl hydroxyethyl cellulose can more easily gain access to the surface of the film. When the film had blushed, the drying was completed with relatively dry .air.

The blushed film produced in Example I is rendered sufliciently transparent by impact or pressure to allow .the dark coating to be visible through the blushed film.

.The legibility' of the copies is dependent upon the convtrast of the opaque and transparent portions of the blushedfilm. This film while having a light reflectance of 77% for a 1% mil thick application, produces considerable contrast when pressure is applied. A 4% con- ,trast in light reflectance is obtained with a pressure of about 880 p.s.i. which is a pressure much less than what.

would be obtained with a typewriter key and is in fact less than a normal pencil pressure. At 3520 p.s.i., the

contrast is 18% and in a manifold of 8 sheets the pres- .sure at the bottom sheet may vary between 1000 and 3000 p.s.i. from a normal typewriter key. The cushioning efiect of the multiple sheets of paper makes the exact measurement of pressure quite difficult and the exact pressure is not known. At 10,000 p.s.i. which is com- 'mon in an ordinary typewriter with 1 or 2 sheets of paper, the percentage of contrast is approximately 42% which gives a very distinct and legible copy.

Example II The following components were mixed and dried in the same manner as given in Example I and the blushed assasoa 7 film provided a white, pressure sensitive fihn having a light reflectance of 77 Lbs. Acetone 25 Ethyl cellulose 7 Methanol 118 Water 7 Example III The following components were mixed and dried in the same manner as given in Example I and the blushed film provided a light reflectance of and pressure sensitivity above about 3000 p.s.i.

. v Lbs. Nitrocellulose 13.8 Acetone "a 5 Methyl alcohol 74.4 Water 4.2

In each case, blushing of the film and pressure sensitivity are aided by blushing the cellulose film in the presence of a humid atmosphere so that moisture condenses on the film.

Example IV The blushing action of, for-example, the film made by Example I can be improved by the addition of a small amount of methyl ethyl ketone. For example, the following composition when mixed and dried in the same manner as Example I gave very good results:

The addition of a small amount of either a weak acid or weak base has also been found to enhance the qualities of the product. For example, when about .15 1b. of 37% by weight hydrochloric acid was added to the composition of Example IV, a white adherent film having a light reflectivity of between 81 and 82% was produced. At 10,000 p.s.i., the film was made transparent so that the area crushed had a reflectivity of between 43 and 44%. Also when about .2 lb. of 58% by Weight ammonium hydroxidewas added to the composition of Example IV, a blushed coating having a reflectivity of between 81.5 to 82.5% was produced. The coating crushed under pressure of 10,000 p.s.i. gave a reflectivity of 47%. Apparently, the acid or base improves the adherence of the film and also permits the film to be dried entirely in a V humid atmosphere.

Example V The preferred formulation employing ethyl hydroxyethyl cellulose has the advantages of being faster drying than the solution of Example I, primarily because of the lower solvent content, and secondly because of the use of the more volatile acetone to replace part of the methanol.

, Lbs. Ethyl hydroxyethyl cellulose, low viscosity 13.6 Acetone 33.6 Methanol 33.6 Benzene 9.6 'Water 9.6

' paper and typed on using an electric typewriter at a 76 pressure setting of number 3, and ten clearly legible copies of the original were reproduced. A ten sheet manifold also prepared from the formulation of this example was used in an International Business Machines accounting machine which applies less pressure than most typewriters; ten clearly legible copies were reproduced.

A small amount of a softener or plasticizer may be used in the composition of this invention if desirable. For example, many resins and hydrogenated rosins may be used.

The blushed cellulose derivative film is quite porous and appropriate control of the coating thickness and the specified factors involved in producing the blushed film may produce films having different qualities. A film having relatively uniform size pores and sufficient permeability is useful as a filtering material. The cellulose blushed film may be coated upon a tissue type paper for this purpose as well as for use in pressure sensitive manifolds.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, for some modifications will be obvious to those skilled in the art.

We claim:

1. The method of forming pressure sensitive record material, comprising: applying a film including a cel1ulose compound in a compatible organic solvent to the surface of a base sheet, drying the film in the presence of moisture condensed thereon to form an opaque lightcolored blushed film sensitive to writing pressure and then substantially completely drying the film.

2. The method of forming pressure sensitive record material, comprising: applying a film including a cellulose compound in a compatible organic solvent to a base sheet having a dark-colored surface, passing warm, humid air containing sufficient moisture to provide a layer thereof on the surface of the film over the film so that moisture from the air is deposited thereon to blush the film, and then drying the film.

3. The method of forming an opaque film, comprising: applying a wet solvent solution of the film including a member of the class consisting of ethyl hydroxyethyl cellulose, ethyl cellulose and nitrocellulose in a compatible organic solvent to a base sheet and drying the film in the presence of a Warm, humid atmosphere containing suificient moisture to provide a layer thereof on the surface ofthe film so as to condense water upon the wet film during initial drying and at least until the film has blushed, and then completely drying the film.

4. The method of claim 3 wherein said base sheet has a dark-colored surface.

5. The method of forming a pressure sensitive recording material, comprising: coating a dark-colored sheet surface with a film of ethyl hydroxyethyl cellulose in a water compatible volatile solvent and drying the film in the presence of a warm humid atmosphere containing sufiicient moisture to provide a layer thereof on the surface of the film so as to deposit moisture on the film during drying to form a writing pressure sensitive blushed light-colored film over the dark surface.

6. The method of forming pressure sensitive recording material, comprising: precoating a dark-colored sheet surface with an adhesive material, applying a film of ethyl hydroxyethyl cellulose dissolved in a solvent including benzene and methanol to the precoated surface, passing warm and humid air containing sufilcient moisture to provide a layer thereof on the surface of the film over the surface to dry the film and to condense moisture upon the film, continuing passing said air over the film until the film has blushed, and then completely drying the film in the presence of warm relatively dry air.

7. A pressure sensitive recording sheet for use in manifolding, comprising: a base sheet, the surface of which is covered by a film including a cellulose compound, said film having been applied to said surface in a compatible organic solvent, dried in the presence of moisture condensed thereon to form an opaque light-colored blushed film sensitive to writing pressure and then substantially completely dried.

8. The pressure sensitive recording sheet of claim 7 wherein said base sheet has a dark-colored surface.

9. A pressure sensitive recording sheet for use in manifolding, comprising: a base sheet which is covered by a film including a member of the class consisting of ethyl hydroxyethyl cellulose, ethyl cellulose and nitrocellulose, said film having been applied to said sheet in a compatible organic solvent and then dried in a warm, humid atmosphere containing sufficient moisture to provide a layer thereof on the surface of the film so that water condensed thereon during the initial drying and at least until said film had blushed to form an opaque lightcolored blushed film sensitive to writing pressure.

10. The pressure sensitive recording sheet of claim 9 wherein said base sheet has a dark-colored surface.

11. The pressure sensitive recording sheet of claim 9 wherein the member of said class is ethyl hydroxyethyl cellulose.

12. A pressure sensitive recording sheet for use in manifolding, comprising: a sheet having a dark-colored surface, said surface having a first coating of an adhesive material and a second coating of a film, said film having been applied in solution form including ethyl hydroxyethyl cellulose and benzene and methanol as solvents, said film having then been dried in a warm, humid atmosphere containing sufficient moisture to provide a layer thereof on the surface of the film so that water was condensed thereon, the presence of said water on the surface of said drying film having caused said film to blush to form an opaque light-colored blushed film sensitive to writing.

References Cited in the file of this patent UNITED STATES PATENTS 

1. THE METHOD OF FORMING PRESSURE SENSITIVE RECORD MATERIAL, COMPRISING: APPLYING A FILM INCLUDING A CELLULOSE COMPOUND IN A COMPATIBLE ORGANIC SOLVENT TO THE SURFACE OF A BASE SHEET, DRYING THE FILM IN THE PRESENCE OF MOISTURE CONDENSED THEREON TO FORM AN OPAQUE LIGHTCOLORED BLUSHED FILM SENSITIVE TO WRITING PRESSURE AND THEN SUBSTANTIALLY COMPLETELY DRYING THE FILM. 